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GENERAL TECHNOLOGY
HYDRO-AIRE
INTERPOINT
LEAR ROMEC
P.L. PORTER
SIGNAL TECHNOLOGY
Keltec
Olektron
Crane Electronics
Power Solutions
SOLUTIONS
Components (Interpoint)
•
•
•
•
•
•
•
•
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Aircraft Electrical Power
Cabin
Fluid Management
Landing Systems
Sensing & Utility Systems
Power
Microwave Systems
Electronic Manufacturing
Microelectronics
DC/DC Converter
Application Considerations
Interpoint Hybrids
Interpoint has been making hybrids since 1969 and is a pioneer in DC-DC
converter hybrid technology
Advantages of Hybrids
•
Hermetically sealed (90% dry nitrogen) – protects from humidity, corrosion,
contaminants, and makes converters less susceptible to arcing at high elevations
•
Completely enclosed, and sealed, in a metal case – reduces radiated EMI when
case is grounded.
•
Uses printed ink resistors – increases power density and eliminates solder
connections.
•
Uses low profile magnetics – improves vibrations
•
No potting material – makes the converters easier to produce, trouble shoot and
provides better thermal performance.
Uses bare die – better heat transfer, higher power density, reduced parasitics,
lighter weight and no hardware required for attachment.
©2006 Crane Aerospace & Electronics
2
Interpoint Hybrids Cont.
Hybrid Assemblies
Cover
Magnetic
Semiconductor
Wire
bonds
Traces / printed
resistors
Solder
Epoxy or solder
Ceramic
substrate
Solder
Thermal epoxy
©2006 Crane Aerospace & Electronics
Header (base plate)
3
Interpoint Hybrids Cont.
©2006 Crane Aerospace & Electronics
4
Reliability
What can be done to insure higher reliability
•
Improve heat sinking. Every 25 degree C temperature rise will decrease MTBF
numbers by approximately a factor of two.
•
Order parts with a higher screening level
Consider flanged parts – a converter bolted down will stand up to shock and
vibration better than a converter whose only means of attachment having their
pins soldered to a PCB. Flanges also provide additional heat sinking.
Non Flanged
Flanged
©2006 Crane Aerospace & Electronics
5
Handling
General Handling Precautions
Parts should be handled carefully to protect the integrity of the compressions seals around the
pins.
A damaged seal, can result in loss of hermeticity.
A bent pin can result in a damaged seal and a cracked substrate.
If a part is dropped the seal can be compromised or the substrate could be cracked.
Never cut an unsupported pin. The
shock may damage the seal. A gauge
block or other tool that slips over the
pin, to provide support, should be used
before cutting.
Once a converter is soldered into a PCB
the solder should have enough support
to cut the pins.
©2006 Crane Aerospace & Electronics
6
Reliability Cont.
Screening table from Interpoint data sheet
More screening translates
to higher reliability
Testing options
Tests performed
(yes/no)
©2006 Crane Aerospace & Electronics
7
Reliability Cont.
Screening table from Interpoint data sheet cont.
Screening affects MTBF results
Screening levels are Standard, ES,
H (883), and K
Standard = x MTBF hours
ES = ~ 2x MTBF hours
H (883) = ~ 4x MTBF hours
K = ~ 16x MTBF hours
” K” screening levels have
approximately16 times the MTBF
hours as a Standard screening
level.
©2006 Crane Aerospace & Electronics
8
Thermal Management Cont.
Magnetic
Semiconductors
Trace
Heat
Sources
Heat
transfer
Thermal epoxy
or solder
Ceramic
substrate
Solder
Header
Customer interface (PCB / Heat-sink)
©2006 Crane Aerospace & Electronics
9
Thermal Management Cont.
The operating temperature refers to the
header (base plate) temperature of the
converter
Heat extraction is through the header.
Interpoint converters are designed to be
conduction cooled.
Heat generating components are
thermally attached to the header, either
directly mounted (magnetics), or
mounted to a ceramic substrate material
that has is thermally connected to the
header.
Steel headers are 0.050in – 0.060in
(1.27mm – 1.52mm) thick providing a
low thermal impedance.
While power dissipation is not uniform
across the header, the temperature delta
on the header should be < 1 - 2°C
©2006 Crane Aerospace & Electronics
10
Thermal Management Cont.
Interpoint converter’s should be de-rated linearly from 100% at
“maximum full load operating temperature” (typically 125
degrees) to 0W at “absolute maximum operating temperature”
(typically 135 degrees C).
Power
Full load
Temperature
-55°C
No load
125°C
©2006 Crane Aerospace & Electronics
135°C
11
Thermal Management Cont.
Our converters do not have a single Tjc and do not require
calculations for junction temperature. What matters is that the
base plate / header does not exceed the “maximum operating
temperature”.
• There is no internal temperature sensing, or over-temperature
shutdown circuitry, built-in to Interpoint converters.
• Power dissipating components are spread out to create an even
heat distribution.
©2006 Crane Aerospace & Electronics
12
EMI
What is EMI?
• EMI is ElectroMagnetic Interference which can be an electric field or a
magnetic field. Electric fields are typically generated from voltage and
magnetic fields are typically generated from currents.
•
Interpoint converters are completely enclosed and, when the case is
grounded to earth, short electric fields to earth ground. This reduces
radiated EMI significantly. Some magnetic fields can escape but are
typically not a problem.
The measurement of EMI is the vector sum, or difference, of CM and DM
noise.
EMI consists of both common mode (CM) and differential mode (DM)
noise. DM noise, also known as normal mode noise, is when the currents
180 degrees out of phase between positive input and input Common. CM
noise is in is typically in phase in the input lines but can have some out of
phase component if the line impedances are not balanced. CM noise is
measured WRT chassis.
©2006 Crane Aerospace & Electronics
13
EMI Cont.
CM noise
CM noise is typically generated by capacitive coupling of power components
to the chassis. During switching the high dv/dt of the power components,
during turn on and turn off, pump currents into the chassis through the
parasitic capacitance. Internally radiated noise conducted to the chassis and
input leads can also become CM noise.
Ceramic
Substrate
Power
Component
Parasitic
Capacitance
Header/Chassis
(heat sink)
Chassis
Connection
©2006 Crane Aerospace & Electronics
14
EMI Cont.
= Switching Power
Components
Cp = Parasitic
Capacitance
ICM = CM current
Typical DC/DC Converter Block Diagram
Common mode currents should be bypassed back to their source. Any current
that is not bypasses back to its source can take the path of the LISN and be
measured.
©2006 Crane Aerospace & Electronics
15
EMI Cont.
How is EMI measured
A device, known as a LISN (Line Impedance Stabilization Network), is used to measure noise
(pollution) in each line. It allows DC to pass and provides a path for high frequency current /
voltage to be measured.
EMI specs are typically concerned with
high frequency noise. The high
frequency takes the path of lowest
impedance. Any current passing
through the 50 ohm resistors (in the
spectrum analyzer) will be measured.
LISN
28V In
28V Out
To Spectrum
Analyzer
Make sure when testing the unused
LISN terminal is terminated with 50
ohms.
To Spectrum
Analyzer
Two things can be done to prevent
noise from being measured
1. Add a high impedance between the
LISN and converter.
2. Add a low impedance to shunt
current away from the LISN
28V Rtn
28V Out Rtn.
Blocks high freq but
allows DC current to pass
Low Z allows high freq
current to be measured
©2006 Crane Aerospace & Electronics
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EMI Cont.
CM Noise - No CM Filtering
I x R measured by
spectrum analyzer
Voltage rising due to
switch turning off
LISN
Converter
Parasitic
capacitance
Current flow
There will be some in-phase and some out-of-phase components depending on the
impedances of the current paths. This shows the main switch turning off. When it
turns on, the current paths will change.
©2006 Crane Aerospace & Electronics
17
EMI Cont.
CM Noise - With CM Filter
Lower I x R
measured by
spectrum analyzer LISN
High Impedance
Converter
Parasitic
capacitance
Current takes path of
least impedance
©2006 Crane Aerospace & Electronics
18
EMI Cont.
DM Noise - No DM Filtering
I x R measured by
spectrum analyzer
High Z (DM)
T
h
i
s
Low Z (DM)
LISN
Converter
Partial EMI filter, internal to converter, reduces ripple
current but not enough to pass EMI specs
©2006 Crane Aerospace & Electronics
19
EMI cont.
DM Noise - With DM Filtering
Lower I x R drop
measured by
spectrum analyzer
DM choke – High Z and
lower ripple current
To DC
source
Converter
LISN
Dampening
network for low Q
©2006 Crane Aerospace & Electronics
Added DM cap – low Z
and stored charge
20
EMI Cont.
•
Keep power traces short and wide and overlap them with their return path.
•
If possible overlap Input Positive and Input Return traces. Overlap Vout with
Output Common. Overlap a clock signal with its return signal. If traces can
not be overlapped keep them as close together as possible - minimize the
loop.
Overlapping traces means one trace runs on one side or the board and the
return path for that trace runs on the other side of the board directly above or
below it. This included Sync and Sync return.
•
Keeping traces short will help reduce radiated noise.
•
Keeping traces wide will add capacitance when overlapping. Wide traces will
also have a slight affect on reducing inductance (although inductance can be
good in some cases).
•
When possible, ground the converter’s case to earth ground to minimize
radiated noise.
©2006 Crane Aerospace & Electronics
21
EMI Cont.
Keep a low inductance / resistive path between filter chassis and converter
chassis to allow the CM noise can take the path of the CM filter caps (internal to
the external filter) to get back to the converter.
Filter
converter
6
1
4
2
3
5
7
C4
???
CM current
Low impedance needed
Keep filter and converter as close together as possible and connect chassis to
earth ground to reduce radiation.
©2006 Crane Aerospace & Electronics
22
EMI Filters Cont.
Try and keep power flow in a straight line. The EMI filtering section should be in a noise free environment.
Placing the EMI, or input section, by the output, or any other noise source, may allow the noise to couple to the
input and be measured.
Loops (no overlapping)
Filter
To LISN
Non Ideal Layout
Converter
Long, thin, traces
Load
Coupled noise is not filtered
Ideal Lay-out
• Short traces
• Wide traces
Vin
Filter
Converter
Load
• Straight flow
• Over-lapping traces
• Good chassis connections
Good chassis connections between filter,
converter, and chassis (earth ground)
©2006 Crane Aerospace & Electronics
23
EMI Filters Cont.
Capitalize on the Parasitics
If parasitics are not considered, a balun (CM choke) will act as a short to DM
currents and act as a high impedance to CM currents.
If using a balun consider segment winding a choke vs. bifilar winding. The poor
coupling will create DM inductance (leakage inductance) free.
The diagrams below show a segment wound versus a bifilar wound CM choke.
Bifilar wound. Low DM inductance and
more likely to have a short between the
2 wires
Segment wound. Free DM inductance (good)
and less likely to have a short between the 2
wires
+28V
+28V Rtn.
Loose coupling between
+28V and +28V Rtn.
©2006 Crane Aerospace & Electronics
Good coupling between
+28V and +28V Rtn.
24
EMI Filters Cont.
Measuring leakage inductance of a CM choke
Short the two Finish ends of the inductor (28V Out to Return Out)
Measure between the two start ends of the inductor (28V In to Return In)
The measured value will be the influence of both windings in series as seen by
the DM noise.
Measure
between both
start leads
Short both
finish leads
©2006 Crane Aerospace & Electronics
25
EMI Filters Cont.
Choosing a filter
• Size the filter for the maximum steady state current at the lowest
input voltage. Maximum converter current = PoutMax / (VinMin x
efficiency). For multiple converters add their currents.
• Surge currents during start up are typically not a concern.
• Check converter and filter data sheets for recommended filter /
converter combinations.
From FMCE-1528
data sheet
©2006 Crane Aerospace & Electronics
26
EMI Filters Cont.
• When using more than one converter with an EMI filter consider syncing converters
to eliminate beat frequencies. Beat frequencies typically occur at frequencies below
most EMI specs but not always.
• If using an external DM capacitor between a converter and filter consider adding a
damping resistor in series with the cap. Modeling results to insure a low Q is
recommended.
• For modeling purposes, filter schematics are typically available in our data sheets.
Converter input filter schematics and EMI filter schematics can be obtained through
Interpoint applications department.
Schematic from
FME28-461 data
sheet
©2006 Crane Aerospace & Electronics
27
Output Filtering
• For reducing DM output noise add DM capacitance at the
output. Adding caps close to output pins of converter can will
keep currents local and help prevent conducted noise from
becoming radiated noise. Adding them at the load will clean up
the noise where it counts.
• For greater noise reduction add an inductor to make an LC
filter. Modeling is recommended to verify a low Q. Don’t forget
to incorporate load capacitance into your model.
• A higher C, and lower L, will decrease the Q of an external filter
(Good). The leakage inductance from a CM choke will typically
provide enough DM inductance to provide excellent results.
An inductor can compromise output load transient performance
(bad).
©2006 Crane Aerospace & Electronics
28
Output Filtering Cont.
A higher C can improve output load transient performance (good) as long
as it does not decrease the BW of the converter too much.
To keep from interacting with the converter’s control loop, external output
LC filters should have their resonant frequencies greater than 100KHz,
or be well damped.
When using an external output LC filter, with a converter that has remote
sensing, always sense before the output choke. Sensing after the output
choke will add two poles to the compensation and could make the
converter unstable.
All high frequency caps should have low ESR/ESL. A larger value, low
frequency cap, and damping resistor, can take care resonance if an
inductor is used as part of the filter.
•
Consider using different value caps. Smaller value caps typically work
better at high frequency and larger value caps work better at low
frequency. A 2.2uF, a 0.1uF and a 0.01uF cap in parallel may provide
better noise attenuation than a 4.7uF cap.
©2006 Crane Aerospace & Electronics
29
Output Filtering Cont.
•
Layout rules for EMI also apply for output noise.
•
With typical measuring techniques CM noise can show up as DM noise.
A CM choke, and CM capacitors, can greatly reduce the apparent DM
noise (CM noise).
•
Bypassing CM noise from Output Common to chassis with ceramic caps
will reduce CM noise. Having a ceramic cap from Input Common to
chassis will help re-direct some of the currents back to the primary if that
is where it belongs. Make sure isolation specs are not being violated
because of this.
If designing a CM filter consider segment winding the balun (CM choke)
to take advantage of the free DM inductance (leakage inductance).
Modeling
• The next few pages show results from making slight adjustments to a
damping resistor of an output filter. It affects the Q and the attenuation of
the output noise. Changes in any component can produce similar results.
•
Modeling is highly recommended for optimization.
©2006 Crane Aerospace & Electronics
30
Output Filtering Cont.
Modeling a filter
L1 will want to interact with the larger 33uF cap which can be dampened by a resistor (R3). The
damping resistor is so small that it does not burn much of energy in L1. This results in a high Q.
High Q
Damping resistor
(variable)
©2006 Crane Aerospace & Electronics
31
Output Filtering Cont.
Modeling a filter Here the damping resistor (R3) is too large and the 33uF cap is affectively not in circuit. The result
is a high Q.
High Q
Damping resistor
(variable)
©2006 Crane Aerospace & Electronics
32
Output Filtering Cont.
Modeling a filter Here the damping resistor is small enough to allow the 33uF cap to interact with L1 yet big enough
to burn the energy in L1. This results in a low Q (desirable) and the attenuation has not suffered.
Low Q (good)
Damping resistor
(variable)
©2006 Crane Aerospace & Electronics
33
Output Filtering Cont.
Before and After results of a MTR2805S (full load) using a filter similar to the one shown in the
previous slide, and an optimized layout. The inductor was a segment wound CM inductor to achieve
a leakage inductance of around 1.5uH. In addition a CM cap was connected from Output Common
to Chassis. Most of the 4mVpp noise shown here is not real as the scope shows 3mV without the
converter on.
Before
After
Scope set to
20MHz BW.
Use barrel of
scope probe for
measurement
App note
©2006 Crane Aerospace & Electronics
34
Line Transients
•
A line transient is a fast, dynamic, change in input voltage.
•
The change in line voltage can be within the converter’s normal operating range or
out of its normal operating range.
•
When operating out of the normal operating range a maximum value, and time, is
imposed.
•
The specified transient value is the maximum input voltage not a value added to
the 28V bus. A 50V transient means the input will see 50V not 50V on top of 28V.
Excerpt from data sheet
Normal operating range
Transient (outside normal
Operating range)
Transient within normal
Operating range
Imposed time
©2006 Crane Aerospace & Electronics
35
Synchronization Usage
The Sync feature allows adjustment of the converter’s switching
frequency by an external clock.
• Noise injected into the sync input can adversely affect converter
performance so place close attention to layout and
recommendations for unused sync pins.
Applications include
-
Concentration of the noise generated by several converters into a narrower
band.
-
Shifting the noise away from sensitive frequencies of a system.
-
Eliminating beat frequencies from parallel converter operation. No sum or
difference frequencies are present. Low frequency noise is not attenuated
significantly by an EMI filter.
©2006 Crane Aerospace & Electronics
36
Synchronization Usage
Customer’s
System
+28V
Converter 1
Filter
Sync out
Sync in
+28V Rtn
Do not connect Sync Return to Input Common of an EMI filter. High frequency
currents run through the filter (noise) and the CM inductor can have several
volts (noise) across it.
©2006 Crane Aerospace & Electronics
37
Synchronization Usage
Customer’s
System
+28V
Converter 1
Filter
Sync out
+28V Rtn
Sync in
• Here we have the Sync Return line going directly to the converter’s Input
Common as desirable. The problem is now you have shorted out the CM
choke in the external filter and the high current on the +28V Return line will
want to return through the Sync Return Trace – not good.
©2006 Crane Aerospace & Electronics
38
Synchronization Usage Cont.
Two converters & filter (recommended connections)
Power (noise)
Customer’s
System
+28V
Converter 1
Filter
Sync in
+28V Rtn
Sync out
Overlap traces to reduce EMI
Overlap traces to reduce EMI
Wind transformer with good
coupling (bifilar) to reduce
leakage inductance
Connections
made directly
to pins of
converter
Converter 2
Sync in
Power traces
(noisy)
Overlap traces to reduce EMI
Dedicated
traces (clean)
©2006 Crane Aerospace & Electronics
39
Synchronization Usage Cont.
•
The application of the Sync signal can cause an output voltage transient. It is
recommended to apply sync while the converter is Inhibited, then release Inhibit.
•
If the converter can not be Inhibited, have the initial Sync signal transition be
negative (i.e. from 5V to 0V). This has been shown to reduce output transients
due to the application of the Sync.
Do not deviate from the recommended sync range or the converter may be
damaged. If the recommended range is from 500kHz to 600kHz a value of
200kHz may saturate magnetics and damage a converter. More benign deviations
may cause the converters to run hot.
If the Sync signal is not being used see data sheet recommendations for unused
pins. Typically, if unused, the Sync pin is connected to Input Common. Although
the converter will most likely run fine when floating following the “unused pin
recommendations” makes the Sync signal less susceptible to noise.
•
See data sheet for recommended amplitudes, duty cycles and frequency ranges.
App note
©2006 Crane Aerospace & Electronics
40
Inhibit Usage Cont.
Primary Inhibit circuit used on many Interpoint converters
Inhibit
External
circuitry
Inhibit should be open circuit for enable, and connected to Input Common for
Primary Inhibit or to Output Common for Secondary Inhibit (check data sheets for
recommendations).
An internal pull-up is present, no external pull-up is needed, or recommended. Do
not apply voltage to the Inhibit pin.
©2006 Crane Aerospace & Electronics
41
Inhibit Usage Cont.
Transitions should be very fast. Do not use capacitors on the
Inhibit pin to delay the rise.
• When using a common connection to inhibit several converters
each inhibit may need to be isolated with a diode. Some converters
already have internal isolation diodes. Check with Interpoint
Applications if in doubt.
App note
©2006 Crane Aerospace & Electronics
42
Current Limit
•
Interpoint converters have current limit points that are typically 115% to 125% of full load.
Check data sheet to be sure.
Interpoint converters typically have a constant current, current limit. As current tries to increase
past the current limit point the output of the converter drops sharply.
Output drops
at current
limit point
full load
120% of full load
Vout
•
Iout
©2006 Crane Aerospace & Electronics
43
Current Limit Cont.
Short Circuit Protection
Short circuit protection is current limit with any output shorted. The output will
limit its current by causing the output voltage to drop. The output voltage, at the
pins of the convert, will be equal to Iout x Rout. Rout is the resistance seen by the
output pins of the converter and Iout is current limit value.
Example
Current limit = 10A
Rout = 0.02ohms (trace resistance and short resistance)
Vout = 0.2V (10A x 0.02 ohms)
•
It is good practice to heat sink for worst case power dissipation. This is may be
during short circuit.
©2006 Crane Aerospace & Electronics
44
Input Impedance
Input filters should have low impedance
Source impedance is the total impedance looking from converter input
pins into the DC source, including the DC source.
Source impedance includes PCB traces, external filters, inrush
protection, DC source and anything else in between. Don’t forget to
consider dynamic impedances (inductors, capacitors)
The total source impedance must be lower than the input impedance of
the converter or the converter can oscillate causing damage to the
converter.
•
A dc-dc converter has a negative input impedance which means that as
input voltage decreases, input current increases. This is the opposite of a
resistive load and at low frequencies the input current will be 180
degrees out of phase from the input voltage
©2006 Crane Aerospace & Electronics
45
Input Impedance cont.
With a converter Pout stays constant and the
input impedance increases proportionally to Vin2
Zin vs. Vin
80
70
60
Vi
n2
/2
0W
Low input voltage (high input current) translates
to low converter input impedance. Compare the
graph of Zin to Iin.
50
40
Zi
n
The input impedance of a DC converter is equal
to Vin2/ Pin.
=
30
Zin
20
10
0
0
©2006 Crane Aerospace & Electronics
10
20
30
40
46
Input Impedance cont.
Consider more than just steady state impedances
Consider converter Input impedance during application of a slow rising input
voltage bus. The converter may turn on at a low voltage (~14V) and the
converter’s input impedance will be lower than at nominal line voltage.
When the converter turns on the output voltage rises very fast. The fast rise of
output voltage will charge any internal output filter capacitance, and load
capacitance. There can also be overshoot during turn on. This rise in output
voltage can create higher Pout than steady state.
• Where possible, reduce input DM inductance and increase input DM
capacitance.
- DM capacitance decreases impedance seen by the converter
- DM inductance increases impedance seen by the converter
- Q is proportional to the square root of L/C (low L, hi C decrease Q)
App note
©2006 Crane Aerospace & Electronics
47
Input impedance continued Cont.
Vin
Vout
Fast rising input
voltage
Rising Vout charges
output filter caps
Iin
Steady state current
(0.5A / div)
Turn on of MTR2805D (10V span voltage with 11.8 ohm load – less than ½ load)
A mercury switch was used to apply an instantaneous voltage to the input of a MTR.
The fast rising output voltage creates a surge current into the output filter capacitor.
This is reflected back as input current. Adding load capacitance will increase this
surge current.
After the output filter capacitor is fully charged the converter operates in steady state
and the input current can easily be calculated.
©2006 Crane Aerospace & Electronics
48
Input impedance continued Cont.
Vin
Slow rising
input voltage
Vout
Low-line-drop-out
PWM momentarily
throttles back due to
overshoot
Iin
High input current due
to low line operation
Steady state
current (0.5A / div)
Turn on of MTR2805D (10V span voltage with 11.8 ohm load – less than ½ load)
DC source comes up slowly and high current is demanded at low input voltages.
The output rises slowly, with input voltage, due to the duty cycle being maxed out at
low input voltage (low-line-drop-out).
Slow rise in output voltage does not create high currents into output filter capacitor.
The output overshoots and causes the converter’s PWM to momentarily turn off until
the output voltage drops to the regulation level.
©2006 Crane Aerospace & Electronics
49
Using the Span voltage
Interpoint’s dual converters can be used as dual outputs or a single output. When
used as a single output this is referred to as the “span voltage”
Example
If a 12V dual is configured as a positive 24V output, the negative output would be
used as Output Common, and the positive output would be used as the +24V
output. Output Common of the converter would be left floating.
If a12V dual is configured as a negative 24V output the positive output would be
used as Output Common and the negative output would be used as the -24V
output. Output Common of the converter would be left floating.
D2
L3
D2
+24V
L3
+12V
D3
+12V
D3
C1
Rtn.
C1
N/C
Rtn.
C2
N/C
C2
D4
D1
System RTN
D4
L4
-12V
D1
System RTN
Float Output Common and use as +24V
L4
-12V
-24V
Float Output Common and use as -24V
©2006 Crane Aerospace & Electronics
50
Using the Span voltage Cont.
Capacitance when using a span voltage
•
When using a dual configured as a single output, the span voltage is capable of
half the load capacitance of each output.
Example
If a 12V dual has a maximum capacitive rating of 100uF on each output, the total
capacitance for the span voltage would be ½ the max capacitance for each output
or 50uF. An easy way to visualize this is to break the output common connection
and the caps are in series which halves their value.
converter
Load
converter
Load
pos_max
100uF
neg_max
100uF
=
©2006 Crane Aerospace & Electronics
Max_load_cap
50uF
51
Maximum Output Capacitance
Load capacitance above maximum rating
•
Adding output capacitance typically increases the output rise time. On some
models it may cause output overshoot at turn on if the capacitance is
significant.
•
Adding output capacitance can also reduce the converter’s BW making it a
little more sluggish to load transients.
•
The maximum output capacitance values range from 10uF(MHF+2812D and
MHF+2815D) to 5000uF.
•
Too large of value can interfere with control loop and can cause undesired
operation.
The SMDs, if available, list the maximums capacitance for Interpoint
converters. All new data sheets will have this information.
©2006 Crane Aerospace & Electronics
52
Load Balance
•
Load balance only pertains to dual converters (not all) and the auxiliary outputs of
triple converters.
•
Typical load balances are 10% / 90%, 20% / 80%, 30% / 70%.
•
When deviating from the load balance spec the negative output can be out of
regulation.
Example
Assume a 20% / 80% load balance spec and a full rated power of 10W (sum of
both outputs).
At full load one output can supply 8W while the complimentary output can supply
2W. If one output is 8W and the other output is 1W the spec would be violated.
At 50% of full rated power (5W) one output could provide 4W if the complimentary
output were at 1W or greater. If the complimentary output went to 0.8W while the
other output was set to 4W the spec would be violated.
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Accessing SMDs - DSCC website
Standard Microcircuit
Drawings, also known as
SMDs, are data sheets
provided by the Defense
Supply Center Columbus
(DSCC) in their format.
They include parameters,
and conditions, that may
not be included on a
Interpoint data sheet.
Shown to the right are
three pages of an 18 page
MSA2805S SMD
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Accessing SMDs - DSCC website Cont.
Enter www.dscc.dla.mil into browser and hit enter
At the bottom of the home page click on “Standard Microcircuit Cross-Reference”
Below shows the screen that should appear and how to access the desired part. In this
case it is the MSA2805S
Select
Vendor PN
Select
Contains
Type in part
number
Click go
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Application Notes
Application Notes
Interpoint has many application notes related to DC-DC converters and filters.
These have a wealth of information that may make the difference between a
successful or an unsuccessful design regardless of whose converters are used.
They user friendly, easy-to-read and in an easy-to-understand format. A list of
our app notes are provided below. We hope to increase this list soon.
DC/DC Terminology
- Provides a glossary of terms used in the industry
- Allows for a better understanding of parameters used in Interpoint’s data sheets.
Designing with a Distributed Power Architecture
- Explains the benefits of using a Distributed Power Architecture
- Explains some of the issues when working with DC-DC converters.
EMI Compliance Statement
- Discusses some of the requirements of Mil-Std-461C
- Addresses which of these requirements Interpoint converters typically meet
EMI Conducted Interference
- Explains what EMI is and how it is generated
- Provides a tutorial on the design of EMI filters
- Explains what can be done to reduce EMI
- Contains precautions such as what happens with an un-dampened filter.
- Explains and cautions about Input impedance issues.
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Application Notes Cont.
Inhibit & Synchronization
- Provides an overview of Interpoint’s Inhibit and Sync circuits including circuit diagrams
- Provides “Do(s)” and “Don’t(s)” when using Inhibit or Sync
- Addresses the use with multiple converters
- Provides Lay-out precautions
Inrush Current
- Provides an overview of the causes of Inrush current
- Explains what can be done to reduce Inrush currents
- Explains input impedance issues and provides precaution
- Provides a schematic of a circuit that can be used to reduce Inrush currents
Mechanical Mounting, Vibration and Shock
- Addresses the handling, including the cutting of pins, of Interpoint converters
- Touches some thermal issues
- Addresses vibration and shock
Measurement and Filtering of Output Noise
- Explains sources of noise
- Explains differences between CM noise and DM noise
- Provides measuring techniques
- Provides solutions for reducing CM and DM noise
- Provides precautions
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Application Notes Cont.
Thermal Management
- Explains how to calculate power dissipation (source of heat)
- Explains convection, conduction, and radiation
- Provide a basic understanding of thermal issues including calculations.
- Explains thermal impedances of Interpoint converters
Transient Suppression
- Briefly touches some transient specs
- Provides some solutions, including schematics, and outlines limitations
- Provides precautions such as damping and impedance imbalances
Link to app notes
http://www.interpoint.com/resources/application_notes
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Application Assistance
Interpoint has a dedicated applications department whose sole purpose is helping customers.
Application Goals
Respond to customers within 24 hours. We can usually be reached immediately by phone.
Provide customers with the answers they need to move forward.
Encourage all questions from the customer and make them feel all their questions are
welcome and important
Always encourage customers to follow up if they are not satisfied with the answers
Provide the best service in the industry!
Application Engineers
Wayne Brown (425) 895-4016
[email protected]
Dennis Koo (425) 895-3002
[email protected]
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Aircraft Electrical Power
Cabin
Fluid Management
Landing Systems
Sensing & Utility Systems
Power
Microwave Systems
Electronic Manufacturing
Microelectronics
www.craneae.com
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